US 7091685 B2 Abstract A closed-loop system
10 is provided for controlling a DC motor. The system includes a DC motor 12, a controller 18 associated with the motor and constructed and arranged to control operation of the motor, a voltage sensor 14 constructed and arranged to measure a voltage supplied to the motor, a speed sensor 16 associated with the motor and constructed and arranged to obtain a measured speed of the motor, and a conditioning circuit 21 constructed and arranged to receive a speed signal and condition the speed signal to provide to the controller, a nominal speed based on the voltage supplied to the motor, or nominal rate of acceleration or deceleration upon a change in the desired speed. The controller 18 is constructed and arranged to compare the measured speed with a certain speed, that is less than the nominal speed, at a voltage corresponding to a measured voltage, and if the measured speed is less than the certain speed, a fault condition is defined by the controller. The controller 18 is also constructed and arranged to compare the measured rate of change of speed with a desired rate of change of speed, that is more than the nominal rate of change of speed in the case of motor acceleration, or less than the nominal rate of change of speed in the case of deceleration, at a voltage corresponding to a measured voltage, and if the measured rate of change of speed differs significantly from the expected rate of change of speed, a fault condition is defined by the controller.Claims(28) 1. A closed-loop system for controlling a DC motor, the system comprising:
a DC motor,
a controller associated with the motor and constructed and arranged to control operation of the motor,
a voltage sensor constructed and arranged to measure a voltage supplied to the motor,
speed measuring structure associated with the motor and constructed and arranged to obtain a measured speed of the motor, and
a conditioning circuit constructed and arranged to receive a speed signal and condition the speed signal to provide to the controller, a nominal speed based on the voltage supplied to the motor,
whereby the controller is constructed and arranged to compare the measured speed with an expected speed, that is less than the nominal speed, at a voltage corresponding to a measured voltage, and if the measured speed is less than the expected speed, a fault condition is defined by the controller.
2. The system of
3. The system of
4. The system of
5. The system of
6. A closed-loop system for controlling a DC motor, the system comprising:
a DC motor,
means for controlling operation of the motor,
means for measuring a voltage supplied to the motor,
means for measuring a speed of the motor, and
means for receiving a speed signal and for conditioning the speed signal to provide to the means for controlling, a nominal speed based on the voltage supplied to the motor,
whereby the means for controlling is configured to compare the measured speed with a certain speed, that is less than the nominal speed, at a voltage corresponding to a measured voltage, and if the measured speed is less than the certain speed, a fault condition is defined by the means for controlling.
7. The system of
8. The system of
9. The system of
10. The system of
11. The system of
12. The system of
13. A method of detecting a fault condition of a closed-loop DC motor system, the system including a DC motor, a controller associated with the motor and constructed and arranged to control operation of the motor, a voltage sensor constructed and arranged to measure a voltage supplied to the motor, speed sensor associated with the motor and constructed and arranged to obtain a measured speed of the motor, and a conditioning circuit constructed and arranged to receive a speed signal and condition the speed signal to provide to the controller, a nominal speed, based on the voltage supplied to the motor, the method including the step of:
obtaining the desired speed of the motor,
measuring the voltage supplied to the motor at the desired speed,
defining a lowest possible desired speed of the motor at the measured voltage, after a speed of the motor has reached a steady-state condition,
measuring the steady-state motorspeed, and
defining a fault condition when the measured steady-state motor speed is less than the lowest possible desired speed.
14. The method of
15. The method of
16. The method of
17. A closed-loop system for controlling a DC motor, the system comprising:
a DC motor,
a controller associated with the motor and constructed and arranged to control operation of the motor,
a voltage sensor constructed and arranged to measure a voltage supplied to the motor,
speed measuring structure associated with the motor and constructed and arranged to obtain a measured speed of the motor, and
a conditioning circuit constructed and arranged to receive a speed signal and condition the speed signal to provide to the controller, a nominal speed at a measured voltage,
whereby the controller is constructed and arranged to 1) determine a measured rate of change of speed based on the measured speed, 2) determine a desired rate of change of speed at the measured voltage, 3) compare the measured rate of change of speed with a limit of the desired rate of change of speed at the measured voltage, and 4) define a fault condition when the measured rate of change of speed deviates a certain amount from the limit of the desired rate of change of speed.
18. The system of
19. The system of
20. The system of
21. The system of
22. The system of
23. The system of
24. A method of detecting a fault condition of a closed-loop DC motor system, the system including a DC motor, a controller associated with the motor and constructed and arranged to control operation of the motor, a voltage sensor constructed and arranged to measure a voltage supplied to the motor, speed sensor associated with the motor and constructed and arranged to obtain a measured speed of the motor, and a conditioning circuit constructed and arranged to receive a speed signal and condition the speed signal to provide to the controller, a nominal speed, based on the voltage supplied to the motor, the method including the step of:
obtaining a desired rate of change of speed of the motor,
measuring the voltage supplied to the motor at the nominal speed,
defining a limit of the desired speed of the motor at the measured voltage, and
defining a fault condition when the measured rate of change of speed deviates a certain amount from the limit of the desired rate of change of speed.
25. The method of
26. The method of
27. The method of
28. The method of
Description This application is based on U.S. Provisional Application No. 60/538,346 filed on Jan. 22, 2004 and claims the benefit thereof for priority purposes. The invention relates to DC motors and, more particularly, to a process of protecting brush or brushless DC motors during overload conditions that may be the result of, but not limited to, seized bearings, snow packing conditions, and load obstructions without the use of current sensing. Brush and brushless DC motors have been used frequently in battery-supplied applications, such as automotive, electric vehicle, forklift, etc. Damage to the motor can be caused by continuing to energize the motor in the event of a locked rotor, or reduced speed conditions that can result from full or partial obstruction of the motor rotor. Under these conditions, damage to the motor or the control mechanism for the motor itself can be the result. In the control of a DC motor, or a DC brushless motor using electronic control means, variable speed is typically achieved through the use of Pulse Width Modulation (PWM). The electronic controller typically receives a control signal (analog or digital) through a control lead to vary the duty cycle of the PWM voltage applied to the motor windings. As a result, the motor speed will vary in accordance with speed control signal. A typical motor speed vs. command signal input is shown in In addition, in a typical PWM driven motor, current, and or temperature of power stage components are also measured in order to determine if the power stage components should be shut down due to an overload condition to protect either the motor, or control electronics. The system voltage can also be measured in order to shut down the motor in the event of an overvoltage or undervoltage condition. For example, in one typical application, it is desired to operate the motor from +9 V to +16 V. Within this range of operational voltages, a separate motor speed vs. control signal duty cycle will be present at any discrete voltage value. This relationship is shown in In some DC motor systems, the motor speed is also measured to indicate whether or not the motor has experienced a locked rotor condition. In many motor control systems, current and/or temperature are used to determine whether of not the motor has experienced an overload condition. Due to the characteristics of the temperature/current measuring conditioning circuitry, however, damage may occur to the motor and/or control circuitry due to the potentially long time constants associated with conditioning circuits. As such, current protection schemes may not protect the motor or control electronics under all foreseeable overload conditions. In addition, the additional circuitry associated with current/temperature limiting circuitry may increase the overall system cost due to the additional components required, as well as the process steps required to ensure repeatable, reliable operation of these circuits across production lots, and all operational conditions. Accordingly, there is a need to provide an overload protection scheme that monitors motor speed at a particular voltage in order to provide reliable protection for both motor and control electronics across the entire operational range of the motor. An object of the invention is to fulfill the need referred to above, in accordance with the principles of the invention; this object is obtained by providing a closed-loop system for controlling a DC motor. The system includes a DC motor, a controller associated with the motor and constructed and arranged to control operation of the motor, a voltage sensor constructed and arranged to measure a voltage supplied to the motor, speed measurement structure associated with the motor and constructed and arranged to obtain the measured speed of the motor, and a conditioning circuit constructed and arranged to receive a speed signal and condition the speed signal to provide to the controller, a nominal speed based on the voltage supplied to the motor. The controller is constructed and arranged to compare the measured speed with an expected speed, that is less than the nominal speed, at a voltage corresponding to a measured voltage, and if the measured speed is less than the expected speed, a fault condition is defined by the controller. In accordance with another aspect of the invention, a method is provided for detecting a fault condition of a closed-loop DC motor system. The system includes a DC motor, a controller associated with the motor and constructed and arranged to control operation of the motor, a voltage sensor constructed and arranged to measure a voltage supplied to the motor, speed measurement structure associated with the motor and constructed and arranged to obtain a measured speed of the motor, and a conditioning circuit constructed and arranged to receive a speed signal and condition the speed signal to provide to the controller, a nominal speed, based on the voltage supplied to the motor. The method obtains the expected, or desired speed of the motor, measures the voltage supplied to the motor at the desired speed, defines a lowest possible desired speed of the motor at the measured voltage, after a speed of the motor has reached a steady-state condition, measuring the steady-state motor speed, and defines a fault condition when the measured steady-state motor speed is less than the lowest possible desired speed. In accordance with yet another aspect of the invention, a method of detecting a fault condition of a closed-loop DC motor system is provided. The system includes a DC motor, a controller associated with the motor and constructed and arranged to control operation of the motor, a voltage sensor constructed and arranged to measure a voltage supplied to the motor, speed measuring structure associated with the motor and constructed and arranged to obtain a measured speed of the motor, and a conditioning circuit constructed and arranged to receive a speed signal and condition the speed signal to provide to the controller, a nominal speed, based on the voltage supplied to the motor. The method obtains a desired rate of change of speed of the motor, measures the voltage supplied to the motor at the nominal speed, defines a limit of the desired speed of the motor at the measured voltage, and defines a fault condition when the measured rate of change of speed deviates a certain amount from the limit of the desired rate of change of speed. Other objects, features and characteristics of the present invention, as well as the methods of operation and the functions of the related elements of the structure, the combination of parts and economics of manufacture will become more apparent upon consideration of the following detailed description and appended claims with reference to the accompanying drawings, all of which form a part of this specification. The invention will be better understood from the following detailed description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts, in which: With reference to The control electronics or controller For steady state operation, the motor controller An overload protection process for a DC motor in an automotive system is shown in For transient motor speed conditions, where an increase, or decrease in the motor speed command has been experienced, there will be a condition when the motor should achieve a target steady state speed in a given period of time. If this speed has not been achieved, then this could be indicative of an overload condition. Thus, in step In addition to protecting the motor and control electronics due to an overload condition, the above-mentioned algorithm could also be used to limit motor speed during sudden changes of motor voltage that may be present in vehicle. Thus, the system Another embodiment of the invention is shown in In any given motor production lot, there will be a tolerance in the steady state speed range, or in the rate of change of speed that will be experienced due to material and process factors. Regarding a motor that drives a fan, the nominal motor speed (with a fan load) can vary +/−10% under full load conditions. As such, any limits set in the protection system The foregoing preferred embodiments have been shown and described for the purposes of illustrating the structural and functional principles of the present invention, as well as illustrating the methods of employing the preferred embodiments and are subject to change without departing from such principles. Therefore, this invention includes all modifications encompassed within the spirit of the following claims. Patent Citations
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